1. Field of the Invention
The present invention generally relates to medical instrumentation and, more particularly, to a system for and method of inserting a device into and/or through body tissue.
2. Description of the Prior Art
The present invention will be described in connection with a microelectrode of the type which is insertable into the blood stream in an artery or into the artery wall at a precisely controlled radial distance. However, as will become apparent from the following description, the invention may be used to insert any appropriate medical device into and/or through body tissue, as well as for other purposes, as will be described hereinafter.
The lack of oxygen within the tissue of the internal wall of an artery is in part believed to be one of the possible causes or contributing factors in the development of atherosclerosis. One phase of research in the field of atheroscloerosis is a series of studies to measure the oxygen content (or oxygen potential pressure) in the artery wall at selected radial distance from the artery center, through which blood flows, as well as within the blood stream. Typically, a reference electrode is inserted into the blood stream at any location and at a spaced-apart location an oxygen electrode is inserted, either in the artery wall or in the blood stream. Researchers recognized the fact that for optimum results the electrode should be made as small as possible so as not to affect the blood flow and/or the content of the oxygen in the artery wall to be measured.
During earlier phases of the research in this field metallic hypodermic needles of very small diameters, e.g. 1-2 microns (.mu.m) were used in fabricating the oxygen electrodes. It was soon discovered that such electrodes were not easily calibrateable and therefore the study results could not be properly interpreted. The primary reason for the difficulty of calibrating such an electrode, is the presence of protein on the metallic needle and the artery outer surface. The electrode interferes with the measurement of oxygen and therefore sets up its own diffusion field, making accurate accumulation of data most difficult.
To overcome this problem an oxygen microelectrode, formed from a glass capillary tube, drawn out to form a long tapering point, with a tip of 1-2.mu.m was developed. Such a microelectrode, hereinafter referred to as the glass microelectrode, is described in an article entitled "A Microelectrode for Measuring Intercellular PO.sub.2 " by W. J. Whalen et al published in J. Appl. Physiol. 23 (5) 798-801, 1967. The glass microelectrode, unlike the electrode with the metallic hypodermic needle, overcomes the calibration problem. However, as pointed out in the article, and as experienced by researchers, who use such a glass microelectrode, the principal disadvantage of the glass microelectrode is its fragility. The glass microelectrode, which is difficult to make and therefore quite costly, tends to break when attempting to pierce the artery wall therewith. Furthermore, even when the glass microelectrode is successfully inserted into the artery wall, quite often the force used during artery piercing and electrode insertion, tends to deform the artery by forming a dimple therein at the point where the electrode is pressed against the artery, which disturbs the oxygen profile across the artery wall. This is most undesirable.
A need therefore exists for a system or arrangement and method with which a glass microelectrode may be safely inserted into an artery wall, without breaking the microelectrode and/or without disturbing the oxygen profile in the artery wall. A need also exists for a system and method for inserting any medical device, e.g., a transducer, into relatively hard or thick tissue, e.g., a heart muscle, at a desired depth with a minimum of force so as not to disturb and/or injure the tissue.